1987 XJ-S V12. I'm hard-wiring the instrument panel (possibly way too much time on my hands) and so-far so-good. But today I ran into something a little baffling.

The wiring schematic shows that there should be a 100 ohm resistor across the alternator light. My understanding is that this resistor is supposed to "excite" the charging circuit. Great.

But when I examine the wiring itself, I don't find a resistor, but do find an in-line fuse holder with no fuse in it. At first blush I would think that would stop something from working, but in the five years or so I've had it I've not had any charging problems.

Nowhere in the electrical guide do I see that this circuit is fused. So I have a fuse holder with no fuse in it, which I would think would stop the circuit from working. Then again, I have a schematic that shows a resistor that I also can't fine.

Can someone clarify?

Sorry its on its side.

Why does this circuit work with no fuse in the holder?

Thanks,

John

 

FWIW.....

On the Series III sedans the resistor isn't in the harness but, instead, cleverly placed in the cavity that holds the bulb socket.

Now, the XJS has a different panel, obviously, but take a peek right in the area of the bulb itself.

As foir exciting the circuit, in most other cars the bulb itself provides the required resistance. I always thought (but never confirmed) that Jaguar added the resistor so that the charging circuit would still work if the bulb failed.

Cheers
DD

 

John
That is something I have long thought about, as I greatly dislike the design of the panel/loom multiplugs. Could you please post a few more details on exactly what you have decided to do?

 

Thanks for that Doug, but no sign of a resistor close to the bulb. Then again, maybe it is one of tape wrapped "things" lurking far enough behind the instrument panel that I can't even get to them to unwrap them.

John

 

Just a few pics of the instrument panel rewire.

Thanks,

John

LED strip lighting. I choose green. The spots of epoxy help hold it on since the adhesive backing doesn't stick all that well.

Instrument wiring is about done. Next come the LED caution and warning lights.

 

DO NOT use LED for the alternator light, this one must be incandescent which is not polarity sensitive.

 

Hi Warjon,

I was thinking of wiring two LEDs "back to back" (so one would always have the correct polarity) to get around that issue. I've not experimented with it yet, but if that doesn't work I'll just throw one of the little light bulbs back into that socket.

Thanks,

John

 

A LED is a diode and works electrically like a diode. A diode is basically an electronic one way tap. If you put 2 taps in series in a water pipe and either is turned off no water will flow.

2 diodes in parallel with opposite polarity should work. If you use discrete LED's you will need to add resistors in series with the LED's.